There's no cast, no visible sign that tells the people around you what a hard day costs you, or what to expect from you when you're in one. Bipolar disorder asks you to monitor yourself, often alone, often at the exact moment you're least equipped to.
And the tools meant to help live apart from each other. A psychiatrist who sees a fraction of your life for a few minutes a month. A mood app that only knows what you remember to log. A habit tracker that sees your actions but not why they slipped. A support circle that cares, but has no structured way to actually see what's happening.
Each piece, on its own, gives a partial picture. None of them talk to each other. None of them talk to you.